Long range ordered state

Spin-spin Coupling, Long-range Ordered States, and Phase Transitions... 

As the temperature is lowered such that kfiT k 9, i.e. I0l/T l, the paramagnetic state should become unstable with respect to some ordered state. According to MFT, for ferromagnetism a transition to a long range ordered state occurs for = 9, where Tc is the so-called critical temperature or the Curie temperature in older literature. In practice one finds that 9IT ranges between at most. For antiferromagnets the... 

To answer this question we need to consider the kind of physical techniques that are used to study the solid state. The main ones are based on diffraction, which may be of electrons, neutrons or X-rays (Moore, 1972 Franks, 1983). In all cases exposure of a crystalline solid to a beam of the particular type gives rise to a well-defined diffraction pattern, which by appropriate mathematical techniques can be interpreted to give information about the structure of the solid. When a liquid such as water is exposed to X-rays, electrons or neutrons, diffraction patterns are produced, though they have much less regularity and detail it is also more difficult to interpret them than for solids. Such results are taken to show that liquids do, in fact, have some kind of long-range order which can justifiably be referred to as a structure . 

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